Asbestos is an important environmental hazard in the U.S. and remains the primary occupational concern in many developing countries. Although asbestos is carcinogenic and induces both bronchogenic carcinomas and pleura and peritoneal mesotheliomas in humans, the underlying mechanisms of fiber carcinogenesis are not known. With the funding support of this grant, the applicant has shown, and for the first time, that asbestos is a potent gene and chromosomal mutagen in mammalian cells and induces mostly large multilocus deletions. These findings provide the first direct link between chromosomal abnormalities that have frequently been demonstrated in vitro and carcinogenicity in vivo. Furthermore, phagocytosis of asbestos by target cells and the resultant oxyradical production are important mechanistic factors in fiber mutagenesis. To extend these findings and to examine how asbestos induces mutations, particularly the origin and types of free radicals involved, the applicant proposed a series of nine specific aims to address four testable hypotheses using the human-hamster hybrid (AL) cell model. The first objective is to determine if nucleus is the direct and immediate target in fiber mutagenesis by the use of enucleated cells followed by rescue fusion with karyoplasts to ascertain the incidence and type of CD59 mutations induced. To show that mitochondrial damage plays an essential role in mediating fiber mutagenesis, we will use mitochondrial deficient cells followed by rescue fusion with cytoplasts to determine both the quantitative induction of oxyradicals as well as mutagenesis. The third and fourth objectives are to determine the role of lipid peroxidation and peroxynitnte anions in fiber mutagenesis. The AL cell line contains only one copy of human chromosome 11 and mutations at the CD59 locus coded by the M1C1 gene located on 1 lpl3 can be readily scored using an antibody complement lysis assay. By using specific DNA probes of other genes that have been regionally mapped to various sites on chromosome 11, the molecular spectrum of mutations induced by either asbestos or glass fiber control will be compared.